Method for preserving mushrooms

ABSTRACT

The invention relates to a method for preserving  Agaricus bisporus  mushrooms, other Agaricus spp. mushrooms, or other mushrooms that lose more than 15 wt % upon blanching, wherein optionally a relatively small amount (relative to the amount of fresh mushrooms) of additional ingredients is used, comprising the following consecutive steps: (a) Inserting clean fresh mushrooms in a plastic laminate bag; (b) Subjecting the bag with mushrooms to vacuum at a pressure of about 300 mbar or less; (c) Sealing the bag while keeping the vacuum; (d) Releasing the vacuum, and (e) Treating the bag with mushrooms at a temperature of about 60° C. or more. In this way a commonly used blanching step—applied before packaging—is excluded, by virtue of which energy is saved and the taste and nutritional value is improved. Thus, the mushrooms are of excellent quality with good taste and flavor and well preserved.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT application numberPCT/EP2012/001903 filed on 3 May 2012, which claims priority fromNetherlands application number 2006738 filed on 6 May 2011. Bothapplications are hereby incorporated by reference in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to a method for preserving Agaricusbisporus mushrooms, other Agaricus spp. mushrooms, and mushrooms thatlose more than 15 wt % upon blanching, wherein optionally a relativelysmall amount (relative to the amount of fresh mushrooms) of additionalingredients is used.

2. Description of the Related Art

Common mushrooms of the species Agaricus bisporus are the most commonlyused mushrooms in Europe, America's and in many Asian countries forhuman consumption. Hence, many methods are described to preserve thefreshness of the mushrooms before sale. Equally, many methods aredescribed to prepare ready-to-use mushrooms; i.e. mushrooms that aretreated in one way or another comprising a cooking step, or preservationmethods for keeping such mushrooms for months.

Known methods include: (1) replacing the air atmosphere with a gaseousmixture that slows down discoloration and maturation of the mushroom,which method is used for the sale of fresh mushrooms (see e.g.US2006/159809); (2) blanching the mushrooms, and thereafter packing andsterilizing (see e.g. EP0564026 or EP2191728); (3) washing anddeep-freezing the mushroom; (4) washing and drying the mushrooms; (5)mashing or grinding (parts) of the mushroom, and treating the mashedmaterial. Several variants of these processes are described in forexample JP-A-6062729, JP-A-6284857 and FR-A-2717989.

Despite the large number of possible ways to treat mushrooms, there isan ongoing request for better quality products and for products with asufficient (refrigerated or ambient) shelf life, in particular for theready-to-use, cooked mushrooms. Ready-to-use mushrooms are in particularused in commercial operations, like foodservice and food manufacturers,and by private consumer families. A process that uses less energy wouldalso be preferred.

Mushrooms, in particular those of which the weight loss is considerableupon blanching, have specific problems in their preparation as theweight loss causes substantial economic loss.

Mushrooms generally need to be washed. Washing with cold water generallyis considered less effective. Hence, the general way mushrooms aretreated is by hot water or steam for about 10 minutes to achieve bothwashing and blanching such that the mushrooms shrink and have less than5 vol % free (air) volume and upon further heat treatment likepasteurization or sterilization would shrink less than 15 wt %,preferably less than 10 wt % and even more preferably less than 5 wt %.Thereafter, the blanched mushrooms are general packed with a brinesolution of which the main ingredient is water and the package withmushrooms is pasteurized or sterilized. The blanching and washing stepwith hot water leads to loss of savory ingredients, loss of nutritionalvalue, leading to reduced taste relative to fresh mushrooms and to asubstantial loss of weight. In particular because of the weight lossproblem, it is common to treat mushrooms with vacuum, and—generally atthe same time—supply water (or water with additives), to replace the airin the mushrooms before blanching (see for example EP0564026 orEP2191728). This treatment indeed lowers the weight loss duringblanching, but it has no positive influence on the taste.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a method to produce ready to use, cooked,preserved mushroom with one or more of an improved taste and flavor,improved nutritional value, and/or an improved use of energy.

The method according to the present invention for preserving Agaricusbisporus mushrooms, other Agaricus spp. mushrooms, or other mushroomsthat lose more than 15 wt % weight upon blanching, wherein optionally arelatively small amount (relative to the amount of fresh mushrooms) ofadditional ingredients is used, comprises the following consecutivesteps:

a. inserting clean fresh mushrooms in a plastic laminate bag;

b. subjecting the bag and mushrooms to vacuum at a pressure of less thanabout 300 mbar;

c. sealing the bag while keeping the vacuum;

d. releasing the vacuum

e. treating the sealed bag with mushrooms at a temperature of about 60°C. or more.

By this vacuum treatment, the air is removed from the mushrooms, butwithout heating and without replacing that space with liquid. Theblanching step of the preserving process is excluded, which means asaving of energy. The mushroom juices and flavors, and the nutritionalvalue that normally disappear during the blanching are saved in theproduct.

According to the present invention, the bag is sealed while undervacuum. Hence, one of the further differences with the prior art is,that usually the free space in the mushrooms is replaced by a liquidbefore further treatment. In the present method, no replacement isadded, nor needed. Moreover, the bag in a normal atmosphere environmentpresses the mushrooms to smaller volume, increasing the effectiveness ofheat transfer in a subsequent step. Furthermore, the conductivity isenhanced because there is no longer an isolating layer between themushroom and the heat source because no air is present around themushrooms.

It is possible, and sometimes preferred, to add additives, like a liquidsavory product, salt, spices, acids or anti-oxidants. Solids may beadded as concentrated solutions or dispersions in water. The amount ofadditional ingredients is small relative to the amount of mushrooms,like for example less than 20 ml per mushroom, and/or less than 30 wt %relative to the mushroom, and preferably even substantially loweramounts. The amounts (weight or volume) are defined relative to freshmushrooms.

After sealing of the bag, the bag with mushrooms will be heat treated tocook the mushrooms. This can for example be done at relatively lowtemperature, such that the content of the bag is pasteurized, or it canfor example be done at high temperature, such that the content iscommercially sterilized. The juices and aroma's that are set free fromthe mushrooms (that cause the weight loss in the conventional processesduring blanching) during the cooking do not disappear from the package,and are preserved in the package. Such juices are valuable ingredientsfor sauces, soups and other dishes.

The resulting mushrooms are of better taste than mushrooms treated in aconventional way, comprising a blanching step before packaging. Theenergy used to prepare the mushrooms is also lowered with respect to thegenerally applied method.

XP-0022664408 (FS-1977-11-J-1596) describes analysis of mashed freshmushrooms, which are vacuum sealed in a glass ampoule, for thedetermination of changes in nitrogen containing substances. Thisreference does not relate to the storage of mushrooms, suitable forhuman consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the invention will be appreciated uponreference to the following drawings, in which:

FIG. 1A shows a schematic cross-sectional view of a vacuum chamber priorto insertion of mushrooms used to implement the method of preservingmushrooms according to the present invention;

FIG. 1B shows a schematic cross-sectional view of the vacuum chamberwith a bag of mushrooms inside the vacuum chamber;

FIG. 1C shows a schematic cross-sectional view of the vacuum chamberwith a bag of mushrooms inside the vacuum chamber wherein the lid of thechamber is closed and vacuum is applied;

FIG. 1D shows a schematic cross-sectional view of the vacuum chamberwith a bag of mushrooms inside the vacuum chamber wherein bag ofmushrooms is sealed; and

FIG. 1E shows a schematic cross-sectional view of the vacuum chamberwith a bag of mushrooms inside the vacuum chamber when vacuum isreleased.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The method of the invention is most suitable for mushrooms with weightloss upon blanching. Most common is the mushroom of the species Agaricusbisporus, and the use of this mushroom is preferred because it is wellhandled in the process according to the present invention. Suitableother Agaricus spp. than Agaricus bisporus include for example AgaricusBitorquis, Agaricus campestris, Agaricus blazei, and Agaricus arvensis.Suitable examples of mushrooms that lose more than 15% by wt uponblanching include oyster mushrooms (Pleurotus ostreatus), strawmushrooms (Volvaria Volvcea), and Enokitake (Flammulina velutipes).

In a preferred embodiment, also the Agaricus spp and more in particularthe Agaricus bisporus used in the current process loses substantialamount of weight upon blanching, and preferably at least 15 wt % uponblanching treatment. Blanching in this definition is understood to be aheat treatment with water of 95° C. during 10 minutes. A substantialamount of loss is about 10 wt % or more, preferably about 15 wt % ormore.

The mushrooms can be used as a whole, but also sliced or diced forexample into slices, stripes or cubicals. Hence, in a further embodimentof the invention, the mushrooms are sliced into slices of between 2-15mm, preferably 2-10 mm, or preferably 5-9 mm, or preferably 3-6 mmbefore applying step (a) of the present invention. Also, the stems canbe separated from the caps, and only the caps used in the process of theinvention. In the remainder of this description, the word “mushroom” isused to denote not only entire mushrooms, but also the sliced or dicedmushrooms, or parts of the mushrooms as used in the process of theinvention.

In the method of the invention, it is preferred, that the mushrooms areclean before inserting them into the bag.

The mushrooms should not be heated beforehand in a way that they wouldlose significant savory or nutritional value, as would be the effect ofblanching.

The most important treatment before packaging is cleaning. Hence, it isnecessary to clean the mushrooms in another way than with hot water orsteam for e.g. 10 min as normally done with the combined cleaning andblanching treatment.

In one embodiment of the invention, either hand cleaning, brushing orwashing with cold water is feasible. However, cleaning with warm or hotwater is possible, if done in a sufficient short time. For example,water of 60° C. can be used to wash the mushrooms, if the washing stepis done within for example one minute. Alternatively, washing byspraying with water of 80° C. or 95° C. for 20 sec or 10 sec with themushrooms on a conveyer belt equally can result in clean mushrooms whilestill the savory and nutritional value is contained in the mushrooms.

In another embodiment of the invention, it is preferred, to usemushrooms that are cultivated in such a way, that no debris is attachedto the mushrooms. Thus, according to a preferred method of the presentinvention, the mushrooms are grown such that the mushrooms afterharvesting do not contain debris.

In yet another preferred embodiment of the invention, the mushrooms arewashed with cold water. In a preferred embodiment of the invention, themushrooms are washed with water of a temperature of less than 40° C.,preferably less than 20° C.

In summary, with respect to a treatment before packaging, the mushroomsare not substantially heat treated before filling the bag withmushrooms, meaning that the mushrooms have lost less than 3 wt %,preferably less than 1 wt % relative to untreated mushrooms, by atreatment before filling the bag with mushrooms. Preferably, themushrooms are used in step (a) without treatment at a temperature higherthan 40° C., preferably not higher than 30° C.

In another embodiment, the method comprises adding additives, eitheradded to the mushrooms before subjecting the bag to vacuum, or into thebag before applying vacuum, or during vacuum treatment. Additives may besavory products, such as salt, a salt solution, mushroom concentrateliquid, spices, and other known savory ingredients like acids or otheringredients. Other suitable additives are anti-oxidants.

Such additives (additional ingredients) preferably are added in arelatively small amount (defined relative to the untreated mushroom). Inone preferred embodiment, an amount is added of less than 20 vol %, andeven more preferred in an amount of less than 10 vol %. Alternatively,the amount of additive is about 20 wt % relative to the mushroom orless, preferably about 10 wt % or less.

It is preferred not to add diluent like water. However, if some minoramount of water is added, this may not be detrimental. An acceptableamount may be about 10 wt % or less, preferably about 5 wt % or less.For example, when mushrooms are washed with cold water, some water maystay adhered to the mushroom. In contrast, the presence of substantialamounts of water, like for example more than 30 wt %—which is common inpreservation of mushrooms in tins or glass jars—increases the heatrequirements for sterilization substantially. Furthermore, such amountsof water dilute the taste of the mushrooms. Hence, water in an amount ofmore than 20 wt % relative to the (untreated) mushrooms are preferablynot added in the present invention.

In one embodiment of the invention, the packaging only contains mushroomwith optionally some small amount of further savory ingredient(s).

In another embodiment of the invention, the packaging contains furthersolid ingredients. In this embodiment, the liquid and savory ingredientsoriginating from the mushroom are preferably at least partially absorbedby the solid ingredients. Suitable solid ingredients are (partly) cookedgrains or grain products, like rice, risotto, pasta and other waterabsorbing foods like dried vegetables. The amount of solid ingredientmay be 2 wt % or more, preferably 10 wt % or more. Generally, the amountwill be 100 wt % or less, preferably about 20 wt % or less.

The plastic laminate bag preferably has good oxygen and water vaporbarrier properties. For example, in case the oxygen barrier is too low,oxygen may enter the package, which may cause oxidation of the content.The requirements for the bag depend on the intended use, and theintended period to keep the mushrooms. In case it is envisaged that themushrooms are used within a few weeks, the requirements for the laminatebag are different than when the product needs to be able to be storedfor e.g. three or twelve months. Pasteurized bags generally haverefrigerated shelf life of 1-6 weeks up to 1-12 months. Sterilized bagsgenerally have an ambient shelf life more than 3 months, depending onthe quality of the bag. For a shelf life 12 months at ambienttemperature or more, an aluminum laminated bag, or comparable, ispreferred.

The size of the bag is not critical, and may be 0.2 L or larger, and isfor institutional use preferably 1 L or larger, and may be for example2, 3, 5 or 10 L. Generally, the size will be smaller than 50 L,preferably smaller than 30 L, like for example 30 or 20 L. In a bag of30 L, 10 kg mushrooms (Agaricus bisporus) can be suitably treated.

Generally, laminate bags are useful, in which at least two layers ofplastic films are adhered to each other. The laminate may comprise morethan two layers. Furthermore, the laminate bag may be printed. Examplesof plastic layers include PET film (polyester-terephthalate), BOPP film(biaxially oriented polypropene), CPP film (cast polypropene), PE film(polyethylene), NY (nylon, polyamide) and the like. The two or morefilms may be directly extruded to each other, or may be laminated withan adhesive, or an adhesive film. Laminates with four, five or morelayers are used in practice. Preferably, the laminate bag comprises abarrier layer which increases the oxygen barrier properties.

Preferred examples of suitable plastic laminate bags include bags thathave at least one layer of PET film, preferably provided with an oxygenand optionally water vapor barrier layer and a PE or CPP film for thesealing. PET is a preferred plastic, as this is resistant totemperatures used during retort (during sterilization). Examples ofsuitable barrier layers on the plastic in the laminate bag include abarrier layer from aluminum, aluminum oxide or silicium oxide, triazineor combinations thereof.

In one preferred embodiment, the barrier layer comprises aluminum, asthat is relatively cheap and has very good oxygen and water vaporbarrier properties.

In another preferred embodiment, the barrier layer comprises aluminumoxide or siliciumoxide, as that is a transparent barrier layer. Atransparent barrier layer has the advantage that a customer actually cansee the content of the package, and that such package can be heated in amagnetron.

Preferably, the laminate bag is retortable, i.e. it is able to withstandsterilizing conditions. After retort, the laminate bag still shouldpossess barrier properties better than the properties of the plasticlayers intrinsically (i.e. without the additional barrier layer).Laminates are available that are retortable. Such laminates generallyhave special adhesives between the plastic layers of the laminate.

In the method according the present invention the vacuum is applied at apressure of about 300 mbar or less, preferably at about 200 mbar orless, and more preferably at a pressure of around 100 mbar. The pressureis defined as absolute pressure. A lower pressure has the advantage thatmore air is removed from the mushrooms before sealing the package, andmore useful product can be delivered to a customer. Generally, thepressure will be higher than about 5 mbar (abs), preferably higher than10 mbar. A very low pressure (abs), i.e. high vacuum may increase costswithout adding much in value.

After vacuum treatment, the bag is sealed, preferably using a meltsealable layer comprised in the laminate bag, by applying heat to astrip of the bag at the top. In an alternative embodiment, the bag issealed using an adhesive, or instead of a heat seal, the sealing of thebag can be done by using an ultrasonic seal or an impulse seal. In anyway, the vacuum should be retained inside the bag.

After release of the vacuum (outside the bag), the mushrooms arecompressed by the air-pressure outside the bag. This has as furtheradvantage that in a subsequent heat treatment the heat is effectivelytransferred to the mushroom, as no air layer causes isolation of themushroom from heating. Because of the practical absence of air,discoloring and burning of the mushrooms during sterilization process isavoided.

In a preferred embodiment of the invention, a second seal is appliedafter release of the vacuum, to increase the security of the closure.

Apparatus for executing the method of the invention are known as such,for example for packaging coffee.

In an alternative way, the bag with mushrooms can be placed outside thevacuum chamber and just the top of the bag inside the vacuum chamber.The vacuum is applied into the bag through a special embossed insidelayer of the bag. This method can be applied—as example—at a verticalflow-pack machine from GKS Packaging.

After packaging in the above described way, the packaged mushrooms aresubjected to sufficient high temperature for a sufficient long time tocause the mushrooms to be pasteurized. Preferably, the mushrooms aresubjected to sufficient high temperature for a sufficient long time tocause the mushrooms to be sterilized. With both treatments, themushrooms may be treated sufficiently long to be “cooked”, and ready forconsumption.

For pasteurization and cooking the mushrooms, it would be suitable toapply a temperature of 60 to 100° C. for 40 to 10 min, for example 20min at 80° C., or 10 min at 100° C. With this range of temperatures, itis not necessary to use pressurized equipment.

For sterilization, it is preferred to apply a temperature between 100and 150° C., preferably between 120 and 140° C., for about 30 to 5 min.For example, a temperature of 125° C. can be used for 15 min. Suchprocess can also comprise two or more steps, in which for example in afirst step, a temperature is applied of 80° C. for 10 min (to shrink themushrooms) and thereafter a temperature of 127° C. for 10 min to achievefull sterilization.

After treatment, the bags can be cooled and stored for sale. Generally,the package will be preprinted. The package can also be provided with alabel, mentioning the content, packaging date, and/or ultimate use dateand the like.

It will be understood by the skilled person, that combinations ofpreferred embodiments of the several steps that are disclosed above,according to the description, are disclosed as well, because it ispreferred to combine preferred embodiments.

FIG. 1 shows a schematic drawing of the vacuum chamber of an apparatusthat can be used to implement the method of the invention. In FIG. 1A,the vacuum chamber (1) is shown, provided with an outlet (2) to be ableto apply vacuum; in FIG. 1B, the vacuum chamber has been provided withthe bag (3) with mushrooms (4). In FIG. 1C, the vacuum chamber (1) isclosed with a lid (5), and vacuum is applied through outlet (2), shownby the arrow. Thereafter, as is shown in FIG. 1D, the bag (2) is sealedby applying a heating element (7, 7′) at the top (6) of the bag, whilestill applying vacuum. Thereafter, the vacuum can be released, as shownin FIG. 1E with the arrow through (2). This causes the bag (3) andmushrooms (4) to be compressed. Thereafter, the bag can be taken out ofthe vacuum chamber for further treatment, like for example adding anadditional seal, and thereafter heat treatment.

The invention will be elucidated with the following, non limitingexamples.

Example 1

In a vacuum packaging machine of Henkovac, a bag (of the basicstructure: PET-Alu-NY-CPP, of retort quality and heat sealable) of 2.5 Lvolume was inserted, with 1000 gram mushrooms of the species Agaricusbisporus that were brushed clean by hand. After closing of the chamber,vacuum was applied down to a pressure of 120-80 mbar (abs). The bag wassealed by pressing a heated strip to the top site of the bag for 6seconds. After release of the vacuum, the bag was taken out of thevacuum chamber. The bag was brought into sterilization equipment (achamber that can be heated to 150° C., can withstand a pressure of 8 barand in which up to 5 bar steam can be added). The bag was treated withsteam at 125° C. for 15 min. The resulting cooked mushrooms occupied 25%less volume than before cooking, and liquid was set free during thecooking process. The liquid originated from the mushrooms. The mushroomsin the sterilized bag had a storage stability of at least twelve month.The content of the bag was tasted by a panel, and compared to the packedcooked mushrooms according to the prior art, and to freshly cookedmushrooms. The taste panel—consisting of 5 people—gave the followingmarks:

Marks (on a scale Treatment 1-10; 10 is best) Remark Freshly cooked 9.0Method according to the 9.0 Very homogeneous taste invention Methodaccording to the 6.5 Less intense taste prior artThe test panel clearly rated the mushrooms treated according to theinvention higher than mushrooms treated according to the prior artmethod.

Example 2

The method as described in example 1 was used, but the mushrooms weresliced into slices of 5 mm thick. The bag was pasteurized by heating thebag for 20 min at 90° C., by which time the mushrooms were shrunk 28%,and fully cooked.

Example 3

The method as described in example 1 was used, but in addition,additives were added, as shown in the following table.

Amount of mushrooms Additive Amount of additive 1.0 kg Soy sauce 10 ml1.0 kg Condensed mushroom savory liquid 10 ml of Scelta Mushrooms 1.0 kgTable salt and dried garlic 10 gram and 5 gram

The mushrooms were tasted by a panel, and were considered at least asgood as freshly cooked mushrooms with the same additives.

What is claimed is:
 1. A method for preserving Agaricus bisporusmushrooms, other Agaricus spp. mushrooms, or other mushrooms that losemore than 15 wt % upon blanching, wherein optionally a relatively smallamount (relative to the amount of fresh mushrooms) of additionalingredients is used, the method comprising the following consecutivesteps: a. inserting clean fresh mushrooms in a plastic laminate bag; b.subjecting the bag with mushrooms to vacuum at a pressure of about 300mbar or less; c. sealing the bag while keeping the vacuum; d. releasingthe vacuum; and e. treating the bag with mushrooms at a temperature ofabout 60° C. or more.
 2. The method according to claim 1, wherein themushrooms are of the species Agaricus bisporus.
 3. The method accordingto claim 1, wherein the mushrooms are grown such that the mushroomsafter harvesting do not contain debris.
 4. The method according to claim1, wherein the mushrooms are not heat treated before filling the bagwith mushrooms, meaning that the mushrooms have lost less than 3 wt %,by any treatment before filling the bag with mushrooms.
 5. The methodaccording to claim 1, wherein the mushrooms are washed with water of atemperature of less than 40° C.
 6. The method according to claim 1,wherein the mushrooms are in a sliced or diced form.
 7. The methodaccording to claim 1, wherein an additive such as a savory product,salt, spice, acid, antioxidant or other ingredient is added to themushrooms or to the bag before subjecting the bag to vacuum, or to thebag during vacuum.
 8. The method according to claim 1, wherein anadditive is present in the bag in an amount of about 30 wt % relative tothe mushroom or less.
 9. The method according to claim 1, wherein waterin an amount of more than 20 wt % relative to the mushrooms is notadded.
 10. The method according to claim 1, wherein the packagingcontains further solid ingredients such as grain and/or dried vegetablein an amount between 2 and 100 wt % relative to the weight of freshmushrooms.
 11. The method according to claim 1, wherein the plasticlaminate bag comprises a layer of PET provided with an oxygen and watervapor barrier layer and a PE, CPP or other plastic layer for sealing,and wherein the laminate bag comprises a barrier layer from aluminum,aluminum oxide or silicium oxide, triazine, or combinations thereof. 12.The method according to claim 1, wherein the laminate bag is retortable.13. The method according to claim 1, wherein the bag is sealed using amelt sealable layer comprised in the laminate bag, by applying a heatseal, ultrasonic seal or impulse seal to a strip of the bag.
 14. Themethod according to claim 1, wherein the bag with mushrooms—aftersealing—is subjected to sufficient high temperature for a sufficientlong time to cause the mushrooms to be pasteurized.
 15. The methodaccording to claim 1, wherein the bag with mushrooms—after sealing—issubjected to sufficient high temperature for a sufficient long time tocause the mushrooms to be sterilized.